The invention relates to an aircraft with jet flap propulsion and as presented in the preamble of claim 1, i.e. an aircraft with an ordinary main plane or a further development hereof as presented in the preamble of claim 2: An aircraft, which in addition to the main plane has a foreplane, a so-called canard plane.
Aircraft with jet flap propulsion have been known for many years, for example from U.S. Pat. No. 2,912,189 or U.S. Pat. No. 2,961,192. Also jet flap propulsion aircraft with a foreplane have been known for years, for example from U.S. Pat. No. 3,362,659. Even aircraft where both the foreplane and the main plane use jet flap propulsion are known, cf. for example U.S. Pat. No. 3,056,566.
In the past several aircraft have been made with special and extensive flap and slot arrangements to reduce stall speed and needed runway. These aircraft are called STOL (short take-off and landing) aircraft. The operating costs of such aircraft are in most cases approximately 30% higher than on conventional aircraft. This lies in added maintenance costs, higher fuel consumption per distance flown. The added wing area (lower wing loading) creates added drag and reduced cruising speed.
Most of all earlier aircraft designers using the blown flap theory have concentrated their efforts on increasing the lift coefficient of the wings to reduce landing speed or to obtain added control force. Blown flaps give extra thrust and this causes problems when the aircraft is being slowed down for landing. In most of the previous patents using blown flaps only a small part of the engine power is used to avoid the problem of extra thrust. If all engine power is used on blown flaps it is necessary to be able to deflect the jet sheet through more than 90 degrees to obtain drag on landing. To be able to deflect air by coanda effect, the outside pressure must balance the centrifugal force of the jet sheet. This is only possible if the radius of the control flap is relatively large compared with the slot height. Furthermore, the duct pressure must be relatively low.